This invention relates to hydraulic jacks and more particularly to a new and improved hydraulic pumping system for jacks and the like.
Hydraulic jacks commonly include a hydraulic ram mechanically coupled to a linkage and a pump operable to deliver hydraulic fluid under pressure to the ram for elevating the linkage. In one type of jack, the pump is manually operable by means of a handle and has a constant displacement for delivering the same quantity of hydraulic liquid to the ram for each handle stroke. This is true both when the linkage is being elevated toward engagement with the load to be lifted and while the lifting operation is in progress. Because of the force normally required to elevate the load is great, hydraulic fluid is delivered at high pressure and low volume. As a result, the linkage is elevated at a relatively slow rate both prior to and after the load is engaged.